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  1. #1

    Default 170,000 miles and misfire - replace all injectors or just the suspect ones?

    I have almost 170,000 miles on my baby and I'm in the final stages of troubleshooting a misifre. No codes are present, but a rough idle (misifre) is felt at 1200-1500 rpm and I'm about ready to start replacing injectors. I can buy a single injector and hope that Cyl #7 is the culprit (which is likely since it threw a code previously and is a major PITA for the LMG engine) or I can replace all eight injectors at the same time and eliminate all the injectors as a cause of the problem and stave off any future issues in that area.

    My dilemma, a single injector is $33, whereas the set of eight are $200 (AC Delco on eBay.) At this stage of the game I'm not sure if a complete injector replacement is a good idea or if the remaining injectors are good for 200,000m plus? I'm sure it's a gamble that the other injectors are 100%, so I'm leaning towards a complete replacement since I can do it myself and it's only an additional $167.00. What do you guys think?

    Note: I've already replaced plugs and wires, cleaned the MAP, replaced the filter, ran two treaments of Lucas and one direct injection of Seafoam. No codes are present, but there's no doubt that I'm getting a misifre somewhere. It's a mystery as to why the ECM isn't picking up on it.

  2. #2

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    If it were me I'd do the work once with all injectors as preventative maintenance. Sure, it's more cash, but it's cash you're going to have to spend not long from now if you don't do it now. For your expense today you also get to rule out the injectors (completely) once you done the work -- if the problem persists, that is.

  3. #3

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    Ok, I'm going to sound picky here, but it's not my intent. I suspect your saying when you are in PARK and you rev the engine to 1200 and 1500 you feel a vibration.

    If you have a mis-fire, the PCM would throw a code.

    No code, I doubt if you have a mis-fire. I suspect you have a mechanical vibration that may feel/sounds like a mis-fire.

    Check things like the motor mounts, the heat shields, maybe a belt driven component with a bad bearing.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

  4. #4
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    can you acess freeze frame and failure records ?fuel trim's at idle , cruise & wide open from fifty above

  5. #5

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    Quote Originally Posted by SurrealOne View Post
    If it were me I'd do the work once with all injectors as preventative maintenance. Sure, it's more cash, but it's cash you're going to have to spend not long from now if you don't do it now. For your expense today you also get to rule out the injectors (completely) once you done the work -- if the problem persists, that is.
    Thank you, this is what I was hoping to read from someone. I was leaning this direction, but wasn't really certain if I was being silly and over-precautious. Thanks for the confirmation!

    Quote Originally Posted by RayVoy View Post
    Ok, I'm going to sound picky here, but it's not my intent. I suspect your saying when you are in PARK and you rev the engine to 1200 and 1500 you feel a vibration.

    If you have a mis-fire, the PCM would throw a code.

    No code, I doubt if you have a mis-fire. I suspect you have a mechanical vibration that may feel/sounds like a mis-fire.

    Check things like the motor mounts, the heat shields, maybe a belt driven component with a bad bearing.
    I can completely understand why you would be asking this question. It's bizarre to me that the engine would not throw codes for this behavior either. And while I'm not a mechanic, I do know the sound of a misfire, and "I feel" that it's almost certainlty that. I even had an independent mechanic confirm my thoughts but they wanted me to try some Lucas before having them do the work.

    The sound, if I can best put it to keyboard is like "putt putt putt putt." I don't think it's a complete missed fire, but perhaps a delayed ignition or something along those lines. I say this because the plugs were all very clean, but #7 had some carbon buildup. Also, the sound (misfire) occurs under load more so than idle. Driving through a low speed parking lot or down my driveway it becomes very obvious. I am also losing about 2mpg from my average as of 5-6 months ago. Also, I should mention that it DID throw codes at one point. I was getting a P0307 and a few other codes related to the evap system. I replaced the evap canister and plugs and wires and cleared the codes. No more codes (5,000 miles and counting) but this misfire (or whatever it is) is still persistent. I've also cleaned the MAP sensor, replaced the ait filter, cleaned the throttle body and every other thing I could think of. I've done everything except replace the injectors and replace the ignition packs.

    With that said, do you still feel that it's not a misifire? Because I would honestly listen to whatever you or anyone else had to say about it. I'm not stubborn when it comes to things like this, but I figured I should give you a bit more info so that you can give it some more thought if you care to spend the time, it would be most appreciated for certain!

    I will check those things you mentioned too...just to be safe. How would you suggest I check the engine mounts? Would I be able to visually see a failure? Engine running or off?

    Quote Originally Posted by sgui View Post
    can you acess freeze frame and failure records ?fuel trim's at idle , cruise & wide open from fifty above
    I assume the answer is no. When you say freeze frames, I assume you mean from a diagnostic machine? I wish I had access to one, as that would really help me out I'm sure. I'm a bit gun shy when dealing with engine shops as I'm not really sure who to trust.

  6. #6
    Sr. Apprentice
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    there's ton's of imformation in the pcm . not many believe in it ......but if read right it will lead you in the right direction

  7. #7
    Sr. Engineer
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    What vehicle are we talking about here? Year, make, model, engine, modifications, etc. I would see if I could get the problem to follow a component, Change the plug out for new, swap coil pack and wire from other cylinder. Don't rule out an EGR problem. If they are leaking a bit they will present as a missfire or bucking at a steady state throttle but go away at slight to heavy acceleration. Check fuel pressure for optimal spray pattern and check compression on the cylinders.
    2000 GMC YUKON SLT, 5.3L tow pkg, G80 rear/w 3.73 gear

  8. #8

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    Quote Originally Posted by Vonderbach View Post
    I will check those things you mentioned too...just to be safe. How would you suggest I check the engine mounts? Would I be able to visually see a failure? Engine running or off? .
    I suggested motor mounts because I thought you were feeling a vibration (the engine shaking), The putt-putt description, does sound like combustion. Maybe the next step is the injector cleaning someone suggested.

    I did do a little searching on the net, it does appear that 170k could be the life expectancy of a set of injectors.
    Ray

    '09 Avalanche LTZ - Black
    '05 Envoy XL (sold)

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